1. Field of the Invention
The present invention relates to a heat exchanger.
2. Description of the Background Art
Heat exchangers, in particular heaters for motor vehicles, have a liquid medium, such as coolant, flowing through them on the primary side, and are exposed on the secondary side to ambient air that is delivered to the passenger compartment. Conventional heaters have a block having tubes and ribs. The air to be heated enters this block and exits it again at its rear. A problem in heating the air in the heater block is that the outlet air temperatures at the air outlet area are not the same everywhere, so that strands of differing air temperature occur. This is a disadvantage for controlled heating of the interior.
A variety of flow patterns are known for flow through a heater, which is generally designed with multiple rows or multiple flows, with the simplest form being parallel flow in which flow passes through all tubes in the same direction. Also known is a U-shaped flow through the heater in which a baffle (transverse baffle) is located in a header tank. Since this redirection of the coolant takes place transverse to the direction of air flow, it is referred to as redirection “across the width.” With respect to the two media flows, coolant and air, this is called a cross-flow. The coolant cools off on the way from the coolant inlet to the coolant outlet, so that the air at the half of the heater on the inlet side is heated more than that on the outlet side half, resulting in the aforementioned strand effect. It is also known to direct the coolant in the parallel direction or counterflow direction to the airflow, in other words the coolant is redirected from one row into the adjacent row in a multiple-row heater. This requires a longitudinal baffle, which separates adjacent rows on one side. This is referred to as redirection “over depth.” Depending on whether the redirection takes place in or opposite to the direction of airflow, this is referred to as parallel flow or counterflow. It is known that better efficiencies can be achieved with counterflow. It is a disadvantage, in particular for relatively wide heaters, that the coolant at the inlet side must be distributed over the full width; this can have the result that flow through the outer tubes is slower with a central coolant inlet, which likewise has an unfavorable effect on the outlet air temperature.
DE 10 2005 048 227 A1, which is incorporated herein by reference, discloses a heater with flat tubes in which the coolant is directed in cross-counterflow to the airflow, which is to say that a redirection in depth takes place towards the air inlet side. In another variant that is not shown and is not described in detail, a redirection in the width is additionally provided.
DE 102 47 609 A1 describes a heater in which the coolant is redirected exclusively in width, and specifically in multiple stages, with multiple coolant flows being connected in parallel. The purpose of this arrangement is to achieve relatively high pressure drops at the redirection points of the water tanks through turbulence of the coolant.
DE 44 31 107 C1 discloses a heater for motor vehicles which operates according to the counterflow principle. In this concept, the coolant is redirected from the air outlet side towards the air inlet side in one or more stages. Better heat-transfer performance can be achieved in this way.
DE 603 06 291 T2 (corresponding to EP 1 410 929 B1) discloses a heater for motor vehicles with separate control of the right and left sides (driver's side and passenger's side) of the passenger compartment. In this concept, the coolant is delivered through two supplies, is redirected to the middle in width, and is removed there through a common return. In a special embodiment (FIG. 8), a redirection in depth is provided in addition to the redirection in width, specifically opposite the direction of airflow. In the so-called left/right control, the airflow exiting the heater is split by a baffle into two partial streams, which are directed toward the left and right sides of the passenger compartment.